SB Strategy:
Take out 4 Balustrade Spy, 4 Undercity Informer, 4 Narcomoeba, Dread Return, Angel of Glory's Rise and Azami, Lady of Scrolls. From there alternate win stacks:

- If you have two cyclers and Doomsday: stack Lion's Eye Diamond, Gitaxian Probe, Manamorphose, Manamorphose, Laboratory Maniac. Cycle to draw the top two cards. Play LED, then Probe, cracking LED in response. Cycle to the bottom of your deck, then cast Laboratory Maniac. If you can draw a card right away, sweet. If not, hope they don't have a removal spell! This is probably the least likely of Doomsday scenarios.

- If you have nothing but a Doomsday, stack Shelldock Isle, Emrakul, the Aeons Torn, and three Lotus Petal: draw a card (preferably by cycling, but maybe through your draw step). Play the Shelldock Isle, putting Emrakul under it. Next turn, play a Lotus Petal to activate the Shelldock Isle, giving you an extra turn. This kill is incredibly vulnerable to lots of things, but at least they are mostly different than the things we normally care about. Karakas, Wasteland, any mill card such as Thought Scour (we only have two attacks with Emrakul), and a flying block and six other permanents are all things we cannot beat.

- If you have a cycler, one mana and a LED (or four mana and a cycler) with your Doomsday: stack Infernal Contract, Lotus Petal, Lotus Petal, Laboratory Maniac, and a cycler. Use your cycler, cracking LED in response to make black mana to cast Infernal Contract and draw the last four cards. Using the one mana from before, cast the Laboratory Maniac with the Petals, and then cycle for the win. If you have Just a LED + cycler, you can pass the turn with Maniac in play just by getting three Petals.

- Finally, the Recross the Paths stack. If you can cast Recross the Paths, your basic pile is LED, cycler, Infernal Contract, LED, LED, Lotus Petal, cycler, Goblin Charbelcher. You need to draw the top two cards either by having a LED in play or having an extra cycler or two in hand.

Alternate SB:
4 Goblin Charbelcher
4 Spoils of the Vault
4 Lion's Eye Diamond
3 Pact of Negation

Strategy:
Take out 4 Balustrade Spy, 3 Undercity Informer, 4 Narcomoeba, Dread Return, Angel of Glory's Rise, Laboratory Maniac and Azami, Lady of Scrolls.

Also consider:
Fiend Hunter (and maybe Thoughtpicker Witch) for a mill win.